1. Field of the Invention
The present invention relates to a DC-DC converter and an organic light emitting display using the same, and more particular to a DC-DC converter and an organic light emitting display using the same to prevent an abnormal display in the organic light emitting display.
2. Description of the Related Technology
Recently, various flat panel display devices having reduced weight and volume, which are disadvantages of a cathode ray tube, have been developed. Flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting display (OLED), etc.
An organic light emitting display among the flat panel display devices displays images using an organic light emitting diode (OLED) generating light by means of the recombination of electrons and holes. The market for such an organic light emitting display has several advantages including excellent color reproduction and thin thickness, etc., has expanded into PDA, MP3, DSC, etc., in addition to cellular, phone applications.
FIG. 1 is a circuit view showing a pixel for an organic light emitting display. Referring to FIG. 1, the pixel comprises a first transistor M1, a second transistor M2, a capacitor Cst, and an organic light emitting diode OLED.
The source of the first transistor M1 is coupled to a first power supply ELVDD, the drain thereof is coupled to the organic light emitting diode OLED, and the gate thereof is coupled to a node N1. The source of the second transistor M2 is coupled to a data line Dm, the drain thereof is coupled to the node N1, and the gate thereof is coupled to a scan line Sn. The first electrode of the capacitor Cst is coupled to the first power supply ELVDD and the second electrode thereof is coupled to the node N1. And, the organic light emitting diode OLED comprises an anode electrode, a cathode electrode and a light emitting layer, wherein the anode electrode is coupled to the drain of the first transistor M1 and the cathode electrode is coupled to a second power supply ELVSS. If current flows from the anode electrode of the organic light emitting diode OLED to the cathode electrode thereof, the light emitting layer light emits corresponding to the amount of the flowing current. The equation 1 represents the current flowing into the drain of the first transistor M1.
                              I          d                =                              β            2                    ⁢                                    (                              ELVDD                -                Vdata                -                Vth                            )                        2                                              [                  Equation          ⁢                                          ⁢          1                ]            Herein, Id represents the current flowing into the drain of the first transistor M1, Vdata represents the voltage of the data signal, ELVDD represents the voltage of the first power supply at the source of the first transistor M1, Vth represents the threshold voltage of the first transistor M1, and β represents a constant.
If the pixel of the organic light emitting display is supplied with the first voltage ELVDD and the second voltage ELVSS even when the data signals is not transferred, a certain voltage is applied to the gate of the first transistor M1 by means of the capacitor Cst. Therefore, current flows into the organic light emitting diode OLED so that the pixel is light emitted. However, this luminescence is unnecessary luminescence so that the lifetime of the pixel is shortened.